Any chance the M5 portion could represent a VIP Marine - well, Navy, obviously - escort mission?
Possibly ... and if this string IS aviation-related, and if M5 means Marine 5 (transport for 5th in the line of Presidential succession), that would indicate Steven Mnuchin, Secretary of the Treasury. But B-8028 is a Chinese registered aircraft ... I'm having difficulty connecting it to Mnuchin and AF1 (apologies for being a newbie at this).